In a cooling system with a network of multiple parallel microchannels and minichannels, each having a hydraulic diameter less than three mm, a liquid used for cooling is introduced. As the liquid flows through the network, initially heat transfer is by convection from the walls of the microchannels and minichannels.
As the liquid flows further downstream through the network, additional heating of the liquid occurs. Eventually, the wall temperature of the microchannels and minichannels rises above the local saturation temperature of the liquid. However, boiling of the liquid does not occur unless there are proper nucleation cavities present. If one or more nucleation cavities are present, nucleation occurs over the nucleation cavity or cavities and the liquid boils. The range of possible nucleation cavities in the microchannels and minichannels can be expanded by the application of a sufficiently high degree of superheat to the microchannels and minichannels.
Prior to this nucleation occurring and during the superheating, the liquid in the microchannels and minichannels, at least in the vicinity of the nucleation sites, becomes superheated. At this point, a bubble present or formed in this liquid experiences a very rapid bubble growth. The rapid bubble growth leads to severe pressure fluctuation in the microchannel or minichannel, which can result in a reverse flow of the liquid. Experimental evidence and a description of the mechanism leading to this instability is described in Kandlikar, S.G. “Heat Transfer Mechanisms During Flow Boiling In Microchannels.” Proceedings of the First International Conference on Microchannels and Minichannels Apr. 24-25, 2003, Rochester, N.Y., USA ICMM2003-1005, S. G. Kandlikar, Editor ASME Publication, 2003, which is herein incorporated by reference in its entirety. The rapid bubble growth may also adversely affect the heat transfer performance, including heat transfer degradation and/or reduction in critical heat flux, of the cooling system.